In a conventional programmable controller (hereinafter abbreviated to "PC"), for example, as disclosed in Japanese Patent Post-Examination Publication No. Hei-1-50923, stage numbers, logical operations, data operation commands, timer commands, etc. have been provided so that judgment is made as to whether a status of a stage in question is set or reset so as to make control on every controlled unit specified by the stage.
However, in the case of controlling stages (lower-level stages) of a system which is in a relationship of subordination to a certain stage (higher-level stage), for example, in the case where lower-level stages are naturally reset when a higher-level stage is in a reset state, it is necessary to provide commands to reset the respective lower-level stages individually. In that case, stage numbers of the lower-level stages have no rules and are scattered, and the number thereof is so large that it has been apt to make a mistake at the time of stating a command. Further, there has been a problem that it is difficult to understand the relationship of subordination at a glance of a program.